Sub panel ground wire size ?


J

jamesgangnc

I'm going to put a subpanel in a garage. I'm going to run #4 copper
off a 70 amp breaker for the hots and neutral. It's about 70 feet and
#6 would probably do but I picked up a partial roll of #4 cheap. But
what I don't know is what the rules are for the ground wire size?
 
J

jamesgangnc

I'm going to put a subpanel in a garage.  I'm going to run #4 copper
off a 70 amp breaker for the hots and neutral.  It's about 70 feet and
#6 would probably do but I picked up a partial roll of #4 cheap.  But
what I don't know is what the rules are for thegroundwiresize?
I never found anyone with an answer for this. How do you figure out
the ground wire size for a subpanel?
 
Ad

Advertisements

J

jamesgangnc

Did you look?  I DAG'dhttp://www.google.com/#hl=en&q=what+size+ground+wire+subpanel
and the first hit answers your question and tells you the relevant
code.  The Terry Love forum hit near the top is also pertinent, as is
this:http://www.codebookcity.com/codearticles/nec/necarticle310.htm
R
Neither one really answers my question for a 70 amp circuit. I saw it
said #8 for 100amp. I've stumbled across other posts that refer to
tables. I'm guessing it's decided by the supply size breaker, not the
breakers in the sub panel. Given #8 for 100amp I'm guessing maybe I
could use #10 for 70 amp? I've got to go about 70 ft so I don't want
to buy any bigger wire than I have to.
 
D

dpb

Neither one really answers my question for a 70 amp circuit. I saw it
said #8 for 100amp....
... Given #8 for 100amp I'm guessing maybe I
could use #10 for 70 amp? ...
Code Sec 250-94 limits minimum size to no less than #8.

Voltage drop tables indicate for 240V you need T rated temperature to
make 75 ft ampacity rating for 70A/2% voltage drop w/ #8 anyway.

I'd pull #6; the initial cost differential is a one-time thing; the
voltage drop savings and peace of mind are forever.

--
 
R

RicodJour

Neither one really answers my question for a 70 amp circuit.  I saw it
said #8 for 100amp.  I've stumbled across other posts that refer to
tables.  I'm guessing it's decided by the supply size breaker, not the
breakers in the sub panel.  Given #8 for 100amp I'm guessing maybe I
could use #10 for 70 amp?  I've got to go about 70 ft so I don't want
to buy any bigger wire than I have to.
If it's a cost question, sell the #4 you got for cheap and buy #6 with
#8 ground. I'd figure the #4 is about twice the price of the #6 so
you probably wouldn't have to go back into your pocket.

The NEC is copyrighted, as are most codes out there. You won't find
them online - just snippets here and there. Even if you had the book
in front of you, it still won't address every situation. That's where
the inspectors come in as they're the guys in the trenches
interpreting the code...for good or bad.

R
 
J

jamesgangnc

If it's a cost question, sell the #4 you got for cheap and buy #6 with
#8 ground.  I'd figure the #4 is about twice the price of the #6 so
you probably wouldn't have to go back into your pocket.

The NEC is copyrighted, as are most codes out there.  You won't find
them online - just snippets here and there.  Even if you had the book
in front of you, it still won't address every situation.  That's where
the inspectors come in as they're the guys in the trenches
interpreting the code...for good or bad.

R- Hide quoted text -

- Show quoted text -
Yes, I've noticed that about the code. Seems stupid, it should just
be on the internet. Sounds like I need to use #8 for my ground to
meet the code I'd rather just go ahead and do that than try to "trade
in" the #4 I have now for different wire. I'm not getting this
inspected but the various building codes are generally good sense so I
try to follow them.
 
Ad

Advertisements

R

RicodJour

Yes, I've noticed that about the code.  Seems stupid, it should just
be on the internet.  
Agreed. It's as stupid as if you had to BUY your 1040 forms. I would
also think that someone could mount a Freedom Of Information act class-
action suit and spank the fookers into open-sourcing code.
Sounds like I need to use #8 for my ground to
meet the code  I'd rather just go ahead and do that than try to "trade
in" the #4 I have now for different wire.  I'm not getting this
inspected but the various building codes are generally good sense so I
try to follow them.
The NEC, while arcane at times, is much more rationale and arbitrary
than a lot of the building code. Some of the local villages around
here adopt modifications to the state code that are so stupid that you
want to cry. 'Luckily' they have part-time building inspectors who
aren't up on the code themselves, so everyone starts in the same place
- in a hole!

I actually had one inspector show up after framing was completed on a
small remodeling job, and ask where the window header was! The
structure was all exposed and there was only one window opening in the
project... I stood there with my mouth literally hanging open and
pointed wordlessly to the area over the window.

R
 
W

Wayne Whitney

The NEC is copyrighted, as are most codes out there. You won't find
them online - just snippets here and there.
Actually, the NEC is available in two places on line:

At <http://www.nfpa.org>, if you register for a free account. The NEC
is known as NFPA 70. If you search their site and go to the web page
for NFPA 70, at the bottom are links for "View this document" for the
2002, 2005, and 2008 versions.

At <http://resource.org/bsc.ca.gov/index.html>, you can find the
California State building codes. The California Electrical Code is
the 2005 NEC with some amendments.

Cheers, Wayne
 
R

RicodJour

Actually, the NEC is available in two places on line:

At <http://www.nfpa.org>, if you register for a free account.  The NEC
is known as NFPA 70.  If you search their site and go to the web page
for NFPA 70, at the bottom are links for "View this document" for the
2002, 2005, and 2008 versions.

At <http://resource.org/bsc.ca.gov/index.html>, you can find the
California State building codes.  The California Electrical Code is
the 2005 NEC with some amendments.

Cheers, Wayne
Thanks for that info. I registered for the free account and viewed
it. Not a very user-friendly way of accessing it - I hate the Java
applet, but, hey, it's free and right from the horse's mouth.

R
 
A

archibald tuttle

responding to
http://www.homeownershub.com/construction/sub-panel-ground-wire-size-16972-.htm
archibald tuttle wrote:

Wayne Whitney wrote:


Actually, the NEC is available in two places on line:
At <http://www.nfpa.org>, if you register for a free account.
nfpa was a bust. they seemed to want $165 for a membership, couldn't find
a link to get a free account. maybe I didn't prospect long enough.
At <http://resource.org/bsc.ca.gov/index.html>, you can find the
California State building codes. The California Electrical Code is
the 2005 NEC with some amendments.
Bingo- gotta respect those legislatures retentive enough to enact this
stuff as statute. I don't think it is legitimate for the the electric
industry to withhold from people rules to which they are subjected. To me
the battle to free the code is like that to free legal decisions which
used to closely held in cyberspace by westlaw and lexis. Thank god for
Findlaw, an early pioneer and google scholar which got many of the older
decisions by OCR I'll guess.

The legislators in california did precisely what I believe the
constitution requires - enact into law those rules which we must follow
rather than delegate to unelected 'experts' what rules we must follow.

Meantime, most electrically focused forums fall all overthemselves to ban
helping homeowners. I'm surprised that none of their fellow electricians
are homeowners. here I thought that was a decent paying blue collar job.
What a great attitude. A help site with no help. Like not helping
homeowners, i.e. nonprofessionals, will make them safer. I have no
problem if professionals choose not to spend their time answering simple
questions over and over for folks who can't google. I have no problem if
the nature of a question reveals that the poster is likely completely out
of their depth that professionals simply suggest - get a professional. I
have no problem if sites want to differentiate between professionals so
you know whether a particular piece of advice is coming from a
credentialed person.

But this snotty protectionist barrier to entry kind of stuff where you
can't even see a code table unless you have a secret decoder ring has got
to stop:

Table 150.122 California Electric Code
Equipment Grounding Conductor
circuit breaker copper aluminum
15 14 12
20 12 10
30 10 8
40 10 8
60 10 8
100 8 6
200 6 4
300 4 2
400 3 1
500 2 1/0
600 1 2/0
800 1/0 3/0
1000 2/0 4/0
1200 3/0 250
1600 4/0 350
2000 250 400
2500 350 600
3000 400 600
4000 500 800
5000 700 1200
6000 800 1200
Cheers, Wayne
cheerio

-------------------------------------
 
Ad

Advertisements

J

John Grabowski

Actually, the NEC is available in two places on line:
nfpa was a bust. they seemed to want $165 for a membership, couldn't find
a link to get a free account. maybe I didn't prospect long enough.


Bingo- gotta respect those legislatures retentive enough to enact this
stuff as statute. I don't think it is legitimate for the the electric
industry to withhold from people rules to which they are subjected. To me
the battle to free the code is like that to free legal decisions which
used to closely held in cyberspace by westlaw and lexis. Thank god for
Findlaw, an early pioneer and google scholar which got many of the older
decisions by OCR I'll guess.

The legislators in california did precisely what I believe the
constitution requires - enact into law those rules which we must follow
rather than delegate to unelected 'experts' what rules we must follow.

Meantime, most electrically focused forums fall all overthemselves to ban
helping homeowners. I'm surprised that none of their fellow electricians
are homeowners. here I thought that was a decent paying blue collar job.
What a great attitude. A help site with no help. Like not helping
homeowners, i.e. nonprofessionals, will make them safer. I have no
problem if professionals choose not to spend their time answering simple
questions over and over for folks who can't google. I have no problem if
the nature of a question reveals that the poster is likely completely out
of their depth that professionals simply suggest - get a professional. I
have no problem if sites want to differentiate between professionals so
you know whether a particular piece of advice is coming from a
credentialed person.

But this snotty protectionist barrier to entry kind of stuff where you
can't even see a code table unless you have a secret decoder ring has got
to stop:

Table 150.122 California Electric Code
Equipment Grounding Conductor
circuit breaker copper aluminum
15 14 12
20 12 10
30 10 8
40 10 8
60 10 8
100 8 6
200 6 4
300 4 2
400 3 1
500 2 1/0
600 1 2/0
800 1/0 3/0
1000 2/0 4/0
1200 3/0 250
1600 4/0 350
2000 250 400
2500 350 600
3000 400 600
4000 500 800
5000 700 1200
6000 800 1200

The "National Electrical Code" is a copyrighted document and cannot be
reproduced without permission from the NFPA who publishes it. There is no
conspiracy to withhold information from the general public. I encourage
do-it-yourselfers to learn the parts of the code that applies to the
particular job that they are working on.

On my web site I reference the particular articles that apply to the work
that I am discussing. I also have links to purchase the code book and other
code reference short cut books as well.

John Grabowski
http://www.MrElectrician.tv
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Top